Interpretive Summary: Lipids and/or waxes function to protect organisms from desiccation. Usual studies involve their role as cuticular surface lipids/waxes on the exterior of insects and their eggs. The cockroach Diploptera punctata is relatively unique in that it carries its embryos internally in a brood sac. It is also unique in the a large amount of waxy material appears to cover the embryos. When embryos are expelled from the mother into saline the waxy material floats to the surface as flakes. In contrast, ovoviviparous embryos not nourished by the mother do not have a copious waxy covering. Thin-layer chromatography and gas chromatography-mass spectrometry were used to show that the major lipid class of the embryos consisted of long-chain methyl-branched hydrocarbons. The composition of this material was compared with the cuticular surface lipids of the female which also consisted of long-chain methyl-branched hydrocarbons. The major components in both embryos and adult female cuticular surface hydrocarbons were mixtures of components with 33 and 35 carbon atom backbones. Methyl-branched tritriacontanes were 35% of female and 59% of embryo hydrocarbons whereas methyl branched pentatriacontanes were 42% of female but only 19% of embryo hydrocarbons. The difference in proportions of the similar hydrocarbons on the cuticular surface of the female and those covering the embryos suggests that the evolution of the nutrient secretion for the embryos was accompanied by selection for a mixture of hydrocarbons that may provide a waxy covering with a lower melting temperature, and that prevents water loss and protects against invasion by microorganisms without preventing the movement of nutrient fluid into the embryos.

Technical Abstract:
In Diploptera punctata, a viviparous cockroach, batches of embryos have a waxy material on the surface and when expelled from the mother into saline it floats to the surface as flakes. In contrast, ovoviviparous embryos not nourished by the mother do not have a copious waxy covering. Thin-layer chromatography showed that the major lipid class of D. punctata embryos was hydrocarbons with lesser amounts of wax esters and long-chain alcohols. The waxy material on the embryos, presumably made by brood sac tissue, and the cuticular surface lipids of adult females had similar elution profiles and chemical composition upon analysis by gas chromatography-mass spectrometry. n-Alkanes were not identified in the adult lipids and only trace amounts were detected on the embryos. However, there were marked differences in amount between the major methyl-branched hydrocarbon components of embryos and adults. The major components on the embryos were a mixture of 3,X-dimethylalkanes (44%) but these were only 29% of adult female hydrocarbons. However, trimethylalkanes constituted 22% vs. 34%, respectively, of the embryo and female hydrocarbons. The major components in both embryos and adult female cuticular surface hydrocarbons were mixtures of components with 33 and 35 carbon backbones. Methyl branched tritriacontanes were 35% of female and 59% of embryo hydrocarbons; methyl branched pentatriacontanes were 42% of female and 19% of embryo hydrocarbons. The difference in proportions of the similar hydrocarbons on the cuticular surface of the female and those covering the embryos suggests that the evolution of copious nutrient secretion for the embryos was accompanied by selection for a mixture of hydrocarbons that prevents water loss and protects against invasion by microorganisms without preventing the movement of nutrient fluid into the embryos.